|Publication number||US4205269 A|
|Application number||US 05/913,269|
|Publication date||May 27, 1980|
|Filing date||Jun 7, 1978|
|Priority date||Jun 9, 1977|
|Publication number||05913269, 913269, US 4205269 A, US 4205269A, US-A-4205269, US4205269 A, US4205269A|
|Original Assignee||Hochiki Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Non-Patent Citations (1), Referenced by (17), Classifications (9)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates to a remote control device for a variable attenuation circuit in a television community receiving system.
A TV amplifier built in a casing is usually provided immediately below a TV wave receiving antenna of a television community receiving system extensively employed today. The amplifier comprises a preamplifier, a main amplifier and a gain control device provided between the preamplifier and the main amplifier, the gain control device being generally controlled by a volume type switch. In most of the amplifiers, the power necessary for operating the amplifier is supplied thereto through a signal transmission coaxial cable from a power supply unit provided in the subscriber's house.
Such conventional community receiving system is shown in FIG. 1, which comprises: a television (TV) wave receiving outdoor antenna 1; an amplifier 2; a power supply unit 3; a television set 4; and a coaxial cable CX.
In FIG. 2, which shows the essential components of the conventional amplifier and the power supply unit, reference character t1 designates an input terminal for receiving a reception wave from an antenna (not shown), and reference character t2 designates an output terminal for the amplified reception wave, the output terminal serving also as a power supply input terminal. Between these terminals, a preamplifier 5, a gain control device 6, a main amplifier 7 and a high-pass capacitor C6 are series-connected as shown in FIG. 2. A choke coil L11, a diode D2 with its polarity as indicated and a DC power supply section 8 (including a voltage smoothing circuit and a constant voltage circuit) are connected between a point P1, between the terminal t2 and the capacitor C6, and ground. The DC power supply section 8 feeds current to the preamplifier 5 and the main amplifier 7. These components surrounded by the one-dot chain line l1 form a community receiving amplifier 2 and are built in a casing except for a knob of the gain control device (not shown), which is provided on the outside of the casing. The amplifier 2 thus formed is provided immediately below the outdoor antenna on the roof. Components surrounded by the one-dot chain line l2 in FIG. 2 form a power supply unit 3 which is disposed in the subscriber's house or at a position in the vicinity of the house to which the subscriber can readily have access. The power supply unit has terminals t3 and t4. The terminal t3 is connected through a coaxial cable CX to the terminal t2 of the amplifier 2, and it serves as a terminal for receiving signals from the amplifier and also at terminal for supplying current to the amplifier. The terminal t4 is to be connected to a television set (not shown). A high-pass capacitor C7 is connected between the terminals t3 and t4. A choke coil L10 and the secondary coil L9 of a transformer are connected in series between ground and a point P2 between the terminal t3 and the capacitor C7. The primary coil L8 of the transformer is connected through a plug to the commercial power supply.
In operation, the 100 V commercial AC power supply voltage is dropped to 20-30 volts by means of the transformer T, which is then applied through the choke coil L10 and the coaxial cable CX to the amplifier 2, where it is applied through the choke coil L11 to the diode D2, as a result of which it is subjected to half-wave rectification and is then applied to the DC power supply section 8. In the DC power supply section 8, the voltage thus rectified is smoothed and is outputted as a constant voltage to operate the preamplifier 5 and the main amplifier 7. Then, a TV wave received by the outdoor antenna is amplified by the preamplifier 5 and main amplifier 7 and then is applied through the coaxial cable CX and the power supply device 2 to the television set.
When it is judged that the level of an input signal to the television set is improper, the level adjustment has to be carried out. In the typical signal level adjustment method, a signal level measuring device is used for measuring an output signal level from the amplifier 2. In this case, someone has to take it to the place where the amplifier 2 is provided, that is, the roof of the house where the outdoor antenna is mounted. At the roof thereof, the measuring device is connected to the output terminal t2 in order to measure the output signal level from the amplifier 2 and then the output level is adjusted at the proper level by means of the operating knob of the gain control device 6. Furthermore, without the measuring device it is necessary to have the cooperation of many persons. For example, according to the instruction of one person who watches a television, another person who has climbed on the roof operates the knob of the gain control device 6 in order to achieve the adjustment. Both of these two methods are hazardous and troublesome. Further, in the conventional methods, the knob of the gain control device is necessarily protruded from the casing for operation, and this is undesirable with respect to water-proofing.
In addition to the above facts, there is a tendency that the length of the connecting cable becomes longer due to growth of the common antenna television system. This causes a decrease in the output signal level. Therefore, the adjustment of the output signal level of the amplifier must necessarily be frequently carried out.
Accordingly, and briefly, an object of the present invention is to eliminate the above described drawbacks accompanying the prior art. More specifically, an object of the invention is to provide a remote control device capable of remotely controlling a gain control circuit, that is, a variable attenuation circuit in a television community receiving system, by operating a switch means of a power supply provided indoors while watching the television, instead of operating directly a knob of the gain control device provided in the vicinity of an amplifier which is normally disposed outdoors.
In the drawings:
FIG. 1 is a block diagram showing a television community receiving system;
FIG. 2 is a schematic circuit diagram showing a conventional amplifier and a power supply unit;
FIG. 3 is a schematic circuit diagram showing an amplifier and a power supply unit according to the present invention;
FIG. 4 is a circuit diagram showing a switch operating section designated by reference numeral 11 in FIG. 3;
FIG. 5 is a circui-diagram showing a control section designated by reference numeral 9 in FIG. 3; and
FIG. 6 is a circuit diagram showing a variable attenuation circuit designated by reference numeral 10 in FIG. 3.
In FIG. 3 which is a schematic circuit diagram showing an amplifier and a power supply unit according to the present invention, the power supply unit 3 surrounded by a one-dot chain line l2 is roughly similar to the conventional power supply unit shown in FIG. 2. However, the former is differnt from the latter in that a switch operation section 11 is connected between a choke coil L10 and the secondary coil L9 of a transformer. Diodes D1 and D3 opposite in polarity are parallel-connected between the terminals t5 and t6 of the switch operating section 11 as shown in FIG. 4. A variable resistor VR is series-connected between the terminal t5 and the diode D3 so as to control current flowing to the variable attenuation circuit in the amplifier 2. More specifically, when a value of the variable resistor VR is placed at the minimum value, current caused by the voltage having one polarity of the commercial power supply input flows through the diode D3 and then it is outputted by the power supply unit. By contrast, when the value of the variable resistor VR is gradually increased, the current decreases in proportion to the variation in the value of the resistor VR. This current is fed to the amplifier 2, and it is employed for controlling the variable attenuation circuit. The other diode D1 is provided for supplying an operating power to the amplifier 2. The diode D1 allows the voltage having the opposite polarity to pass therethrough to the amplifier 2.
In the amplifier 2 which is surrounded by a one-dot chain line l1 in FIG. 3, instead of the gain control device 6 shown in FIG. 2, a bridged T type variable attenuation circuit shown in FIG. 6 and described hereinafter is connected between the preamplifier 5 and the main amplifier 7. Furthermore, a diode D4 having its polarity as indicated and a rectifier 12 are connected in series between a point P3, between the choke coil L11 and the diode D2, and ground. A control circuit 9 is provided at the output side of the rectifier 12.
In FIG. 5 which shows a circuit diagram of the above mentioned control circuit 9, there are provided two input terminals t10 and t11 the former of which is connected to the emitter of a switching transistor Tr1 and the latter of which is connected through a resistor R6 to the base of the transistor Tr1. A resistor R5 is parallel-connected between the emitter and the base of the transistor Tr1. The collector of the transistor Tr1 is connected through a resistor R7 to the base of a transistor Tr2 and is further connected through a resistor R8 to the base of a transistor Tr3. The emitter of the transistor Tr2 is connected to the input terminal t10 and the emitter of the transistor Tr3 is connected to ground. Furthermore, the collectors of the respective transistors Tr2 and Tr3 are connected to a common output terminal t9.
In operation, when the resistance value of the variable resistor VR included in the switch operating section 11 is increased, electric potential at the point P4 of the control circuit 9, that is, the base potential of the transistor Tr1 increases. As a result, the transistor Tr1 will be turned-off and electric potential at the point P5 between the resistors R7 and R8 becomes that of ground. Accordingly, the transistor Tr2 turns-on and the transistor Tr3 turns-off, as a result of which positive voltage +V which is almost equal to that of the DC power supply section 8, is outputted from the output terminal t9. By contrast, when the resistor value of the variable resistor VR is reduced, the potential at the point P4 of the control circuit decreases, as a result of which the transistor Tr1 turns-on and the electric potential at the point P5 becomes almost equal to the positive voltage +V. Accordingly, the transistor Tr2 turns-off and the transistor Tr3 turns-off, as a result of which a voltage which is almost equal to that of ground, is outputted from the output terminal t9.
In FIG. 6 which shows the circuit diagram of the bridged T type variable attenuation circuit 10, reference characters t7 and t8 designate TV wave input and output terminals, respectively. A series-circuit of a capacitor C1, a pin diode PD1 having its polarity as indicated and a capacitor C4 is connected between the input terminal t7 and the output terminal t8. A series-circuit of a capacitor C2, a resistor R1 and a choke coil L2 for blocking a high-frequency signal is connected between a point P6, between the capacitor C1 and the pin diode PD1, and ground. A choke coil L1 for blocking a high-frequency signal is connected between the point P6 and the input terminal t12. A series-circuit of a capacitor C3, a resistor R2, a pin diode PD2 having its polarity as indicated and a capacitor C5 is connected between a point P7, between the pin diode PD1 and the capacitor C4, and ground. A point P9 between the resistor R2 and the pin diode PD2 is connected to a point P8 between the resistor R1 and the choke coil L2. Furthermore, a series-circuit of the resistors R3 and R4 is connected between a point P10, between the pin diode PD2 and the capacitor C5, and the point P7. A point P11 between the resistors R3 and R4 is connected to an input terminal T13.
In operation, in the case where it is judged that an input signal level to the television is high while watching the television, the resistance value of the variable resistor VR included in the power supply unit 3 is increased, as a result of which a voltage which is almost equal to the output voltage +V of the DC power supply section 8 is outputted from the output terminal t9 of the control circuit 9 and it is applied to the input terminal t13 of the variable attenuation circuit 10. On the other hand, the positive voltage +V of the DC power supply section 8 is also applied to the input terminal t12. Under this condition, a biasing current I1 for biasing the pin diode PD1 which flows in the path of t12 →L1 →PD1 →R3 →t13, is small and a biasing current I2 for biasing the pin diode PD2, which flows in the path t13 →R4 →PD2 →L2 →ground, becomes large.
As is apparent from the characteristics of a pin diode, the alternating resistance, that is, the resistance against the TV wave signal of the pin diode PD1 is large. By contrast, an alternating resistance of the pin diode PD2 is small. Accordingly, the attenuation factor becomes large, as a result of which the output signal level ouputted from the terminal t2 of the amplifier 2 is attenuated, that is the input signal level inputted to the television is attenuated and is adjusted to a proper level.
When it is judged that the input signal level inputted to the television is lower than a proper level, the resistance value of the variable resistor VR is decreased. According to the decreasing of the resistance, the voltage which is almost equal to that of ground is outputted from the output terminal t9 of the control circuit 9 and it is then applied to the input terminal t13 of the variable attenuation circuit 10. On the contrary, the positive voltage +V outputted from the DC power supply section 8 is applied to the input terminal t12. Under this condition, the biasing current for biasing the pin diode PD1, which flows in the path of t12 →L1 →PD1 →R3 →t13, is large. By contrast, the biasing current I2 for biasing the pin diode PD2, which flows in the path of t13 →R4 →PD2 →L2 →ground, is small. As a result, the alternating resistance of the pin diode PD1 is small and the alternating resistance of the pin diode PD2 is large. Accordingly, the attenuation factor becomes small and the output signal level outputted from the terminal t2 of the amplifier 2 increases. Consequently, the input signal level to the television increases and is adjusted to the proper level. Therefore, according to the present invention, it is possible to adjust the output signal level of the amplifier to the proper level by operating the variable resistor included in the power supply section provided indoors while watching the television. Consequently, the subscriber can always watch the television under the best conditions.
As was described before, heretofore if the controlling knob of the attenuation circuit provided in the amplifier is operated to adjust the TV wave input signal level to the proper level, the troublesome operation of someone climbing up on the roof to operate the knob must be carried out. However, according to the present invention, it is possible to freely adjust the input TV signal level to the proper level from inside the building without special lines and devices, merely by adding a simple circuit to the conventional amplifier and power supply unit. In the conventional method, the knob for adjusting the input TV signal level is necessarily protruded from the casing for operation; however, this is undesirable with respect to water-proofing. On the other hand, in the present invention, it is unnecessary to provide the amplifier with the protruded knob therefrom and, therefore, the water-proofing of the casing can be made perfect. Furthermore, even if the number of the television sets sharing the system increases and the television sets are moved from one plate to another, according to the present invention it is very easy to adjust the TV wave input signal. The variety of advantages of the present invention should be well appreciated.
It should be appreciated that various changes and modifications could be made to the embodiment shown and described without departing from the spirit of the invention, for example, the generation of a signal for controlling the variable attenuation circuit could be performed in response to the absence, rather than presence of one half of the power signal. Also, the positive rather than negative half cycle could be used to control attenuation. Furthermore, a number of equivalent circuits for converting the half cycle AC signal to a DC control signal could be used in place of the diode D4, rectifying and smoothing circuit 12 and control circuit 9.
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|US4512033 *||Nov 29, 1982||Apr 16, 1985||C-Cor Labs, Inc.||Remote level adjustment system for use in a multi-terminal communications system|
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|CN102130724A *||Dec 30, 2010||Jul 20, 2011||常熟市高事达光电科技有限公司||Light automatic gain control circuit used for cable TV network optical receiver|
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|EP1011195A2 *||Dec 10, 1999||Jun 21, 2000||Nec Corporation||Variable attenuator system for controlling level of received signal in VSAT|
|WO1998043417A1 *||Mar 25, 1998||Oct 1, 1998||Ntl Technologies Inc||Wireless receiving subsystem with antenna and switchable amplifier|
|U.S. Classification||725/149, 455/232.1|
|International Classification||H04Q9/00, H03G7/00, H04B3/44, H03G1/02, H04N5/00|